1. Field of the Invention
The invention relates in general to methods of performing thermodynamic cycles for generating mechanical and electrical power, and for heating, or cooling.
2. Description of the Related Art
The prior art includes combustors and combustion systems that use diluents to cool combustion, but which provide with relatively poor control over the peak fluid temperature and little spatial control over the transverse fluid temperature profile (or distribution). Cooling of the combustion products has commonly been done with excess air. Pressurizing or compressing this excess air commonly consumes 40% to 85% (from large turbines to microturbines) of the gross turbine power recovered resulting in low net specific power. I.e., the gross power less compressor and pump power produced per mass flow through the compressor(s) or turbine(s).
Conventional applications of diluent have particularly focused on controlling emissions, flame stability and flame quenching, especially when using ultra-lean mixtures and operating near a combustion limit. (E.g., see Lefebvre, A., “Gas Turbine Combustion”, Hemisphere Publishing, 2nd ed. (1998) ISBN 0-89116896-6, section 5-7-3; Bathie, William W., “Section 5.8 Evaporative—Regenerative Gas Turbine Cycles”, 2nd ed., ISBN 0-471-31122-7 (1996), John Wiley & Sons, p 139; Boyce, Meherwan P., “Gas Turbine Engineering Handbook”, 2nd ed., ISBN 0-88415-732-6 (2002), Gulf Publishing Company, p 62; Lindquist, Torbjorn, “Evaluation Experience and Potential of Gas Turbine Based Cycles With Humidification”, Doctoral Thesis, Division: Thermal Power Engineering, Department: Heat and Power Engineering, Lund University, Sweden (2002), p 85). Other efforts to reduce the use of excess air as diluent have employed forms of thermal diluent with higher heat capacity than air, such as steam and CO2, that can remove more heat with less compression work (e.g., Ginter, U.S. Pat. Nos. 3,651,641, 5,627,719, 5,743,080, and 6,289,666 mentioned above, Ginter U.S. Pat. No. 5,271,215, and Cheng U.S. Pat. No. 6,370,862).
Temperature control in multiple locations in the thermodynamic cycle is important for efficient operation. Controlling the peak temperature and profile of the energetic fluid delivered to an expander results in better efficiencies of the cycle (Gravonvski, A. V., et al., “Simulation of Temperature Field Redistribution Through Multi-Stage Cooled Turbines”, 2001-GT-0576, ASME Turbo Expo, 2001, New Orleans). It is difficult, however, to control the temperature profile using excess air or steam as customarily employed to cool cycle components and special mixing devices. The irregularities in the spatial and temporal temperature distribution of flows require greater design margins than preferred to compensate for the large uncertainties in the temperature profiles. (E.g., Malecki, Robert E., et al, “Application of and Advanced CFD-Based Analysis System to the PW600 Combustor to Optimize Exit Temperature Distribution—Part 1”, Proc., ASME, Turbo Expo, 2001). The problem of temperature irregularities is heightened by changes in work load or variations in ambient conditions.
Various thermodynamic cycles have been proposed to improve heat recovery and system efficiency. The conventional Combined Cycle (CC) utilizes a Heat Recovery Steam Generator (HRSG) to generate steam by heat exchange with expanded fluid formed by expanding energetic fluid through a first turbine. The generated steam is expanded through a second (steam) turbine. This results in high capital costs from two turbines. Consequently combined cycles are designed to mostly be used in base load applications. However, deregulation is requiring increasing cyclic power generation. In the Steam Injected Gas Turbine (STIG) cycle, steam is generated in a similar HRSG and is injected upstream of the expander. This uses the same gas turbine with a higher energy per unit mass flow. By only delivering steam, the STIG cycle is limited in its ability to recover lower temperature heat. High water treatment costs and water availability are often stated as a major objections to more widespread use of the STIG. The CHENG cycle is similar to the STIG cycle and with similar objections.
The Recuperated Water Injection (RWI) cycle utilizes a recuperator to recover heat from expanded fluid into incoming compressed air. It may water injection on the intake of the recuperator to improve heat recovery. This is typically limited by an air saturation limit. The Humidified Air Turbine (HAT) cycle humidified intake air through a saturator. The Evaporated Gas Turbine (EvGT) is a similar cycle. While utilizing lower quality water, the HAT and EvGT cycles are limited in the amount of deliverable diluent by one or more air saturation limits. An EvGT cycle has been demonstrated at LUND University in Sweden. Otherwise these RWI, HAT, and EvGT cycles have been little used, possibly because of relatively high capital costs. The HAWIT cycle has been proposed to reduce capital costs. It utilizes direct contact heat exchangers to reduce the cost of surface heat exchangers used in the HAT cycle. It has lower costs but lower efficiency than the HAT cycle. The relative efficiency and internal rate of return for these cycles were compared by Traverso, Alberto, “Thermoeconomic Analysis of STIG RWI and HAT Cycles With Carbon Dioxide (CO2) Emissions Penalty”, Tesi di Laurea, Università di Genova (DIMSET), 2000.
Conventional heat recovery methods have particular difficulty in recovering useful heat below the temperature of steam recovered by heat exchange with the expanded fluid with sufficient pressure to reinject upstream of an expander, or within a steam expander. Much heat energy continues to be lost as the expanded fluid is exhausted. Conventional methods of recovering heat from the expanded fluid (after the hot energetic fluid has been expanded to extract mechanical energy) often seek to use high temperature recuperators to heat the large volume of excess cooling air. E.g., air to air recuperators approaching 700° C. These result in high cost and expensive maintenance, where the recuperator alone may exceed 30% of system costs and 80% of the maintenance in micro-turbines.
Using diluents other than air have resulted in further expenses in diluent supply and recovery in relevant cycles for power generation such as “wet” or humid cycles like STIG and HAT. Conventional cycles with typical heat and/or diluent recovery systems need to add “make-up” diluent to compensate for inefficiencies of the system and to reduce operation costs.
Thermodynamic cycles that use a diluent beyond the oxidant containing fluid often need to recover that thermal diluent for pollution and/or economic reasons, as for example, in Italian Patent TO92A000603 to Poggio and Ågren, N., “Advanced Gas Turbine Cycles with Water-Air Mixtures as Working Fluid”, Doctoral Thesis, KTH, Stockholm, Sweden, 2000). Such processes have been expensive. Make-up diluent is commonly needed because of inefficiencies in the recovery process (Blanco, G. and Ambs, L., “Water Recovery Systems for Steam Injected Gas Turbines: an Economic Analysis”, Proc. 15, Int'l. Conference on Efficiency, Costs, Optimization, Simulation and Environmental Impact of Energy Systems, Berlin, 2002).
In the addition of a thermal diluent, fluid filtering and cleanup has been required to prepare the diluent to be delivered to the thermodynamic cycle system (Ågren, N., op. Cit. (2000); SPE Mashproekt, “Aquarius Cycle”, Nikolaev, Ukraine (http://www.mashproekt.nikolaev.ua). Such conventional methods add substantial expenses.
Pollutants are becoming a common concern throughout the world and their control is becoming more important. Relevant art methods of adding water often exacerbate formation of some pollutants, such as CO, while decreasing others, such as NOx. (E.g., See Lefebvre, 1998, p 337 on CO vs NOx). Control of pollutants to stringent legislated methods has often required additional components at substantial further capital and maintenance costs. Many of these pollutant control devices have short lives compared to the overall plant life resulting in further maintenance expenses. Major firms appear to have made a concerted effort to shift to dry excess air to achieve low NOx emissions and to avoid the use of steam as diluent.
Conventional wisdom discourages water injection into turbine power systems (e.g., Lefebvre op. Cit. 1998, p 337). The cost of providing and treating water is frequently claimed to be a substantial hindrance. Commentators expect efficiencies to drop as more water or steam is added to the cycle (e.g., Pavri, Roointon and Moore, Gerald, “Gas Turbine Emissions and Control,” GE Technical Document No. GER4211, 2001, p 18, www.gepower.com).
Thermodynamic cycles are sometimes used for both mechanical power and heating. The heat produced by the combustion process may be used for heat in assorted applications from steam production to district heating. These “combined heat and power” (CHP) applications have been limited by the design of the CHP device. If the demand for heat or power deviates from the design of the CHP system, the efficiencies may be greatly reduced, especially when providing hot water.
Thus, a need clearly exists for improved energy conversion systems and thermodynamic cycles, which provided reduced system life cycle costs and emissions and improved performance and reliability. There is similar need for improving the thermodynamic efficiency and reducing expenses while maintaining or improving limitations imposed by equipment, environment, including turbine blade life, and pollutant emissions. The present invention seeks to meet these needs.